Conventional CD (Compact Disk) reproducing devices employ a digital-analog converter of the oversampling method. This digital-analog converter performs interpolation operation for digital data discretely input, employing a sinc function or the like. However, this sinc function converges to 0 at ±∞, and has a shortcoming that if the arithmetic operation is truncated at the finite value, a truncation error occurs in the operation. Generally, a stepwise waveform obtained in the interpolation operation is passed through a low-pass filter, but there is also a drawback that a phase distortion or a distorted output waveform may arise through the low-pass filter.
Particularly, in the above interpolation operation using the sinc function, a method is taken in which the values of the sinc function are stored in a table, and read as needed, or held as the tap coefficients for a digital filter, but this method has a problem that the configuration is complex. Therefore, an interpolation circuit capable of performing interpolation operation with a simple constitution is desired.